“It is a very, very volatile business in terms of supply and demand. The oil price responds to very small mismatches between supply and demand,” he told BBC Radio 4’s Today programme.
The price of oil has roughly halved in the past year, to around $50 (£32) per barrel.
Goldman Sachs predicted earlier this month it could fall as low as $20.
When asked where oil prices may go next, he told the BBC: “The honest answer to that is I don’t know.”
The halving of the oil price is “on the back of just a few percent of oversupply, and it shows how inelastic the whole system is, and simply because oil is so cheap – its not as if demand is going to respond,” he said.
He added that oil becoming cheaper would not tempt consumers to use more of it, as can happen with other products.
“People don’t drive to work twice because it’s more economical to do so” than it was before, he explained.